with 0.1 mg of Superase (protease from Pfizer) per ml for 4 hr at 60 C. After incubation the mixture was heated for 7 min

Transcription

1 Proc. Nati. cad. Sci. US Vol. 84, pp , June 1987 Biochemistry Heparin sequences in the heparan sulfate chains of an endothelial cell proteoglycan (heparitinase I/heparitinase ih/heparinase/copolymer/disaccharide sequence) H. B. NDER*, C. P. DIETRICH*, V. BUONSSISI, ND P. COLBURN W. lton Jones Cell Science Center, Lake Placid, NY Communicated by Gordon H. Sato, January 13, 1987 BSTRCT The structure of the glycosaminoglycan chain of a heparan sulfate proteoglycan isolated from the conditioned medium of an endothelial cell line has been analyzed by using various degradative enzymes (heparitinase I, heparitinase II, heparinase, glycuronidase, sulfatases) from Flavobacterium heparinum. This proteoglycan inhibits the thromboplastinactivated pathway of coagulation; as a consequence, the catalytic conversion of prothrombin to thrombin is arrested. Heparitinase I (EC ), an enzyme with specificity restricted to the heparan sulfate portion of the polysaccharide, releases fragments with the electrophoretic mobility and the structure of heparin. Conversely, an assessment of the size and distribution of the heparan sulfate regions has been provided by the use of heparinase (EC ), which, by degrading the heparin sections of the chain, releases two segments that exhibit the structure of heparan sulfate. One of these segments is attached to the protein core. On the basis of these findings, the heparan sulfate chain can be defined as a copolymer containing heparin regions in its structure. The combined use of these enzymes has made it possible to establish the disaccharide sequence of parts of the glycosaminoglycan moiety of this proteoglycan. Heparan sulfate proteoglycans are complex macromolecules that consist of a protein backbone to which heparan sulfate chains are covalently linked (1). They are ubiquitous compounds found in a wide variety of vertebrate and invertebrate tissues (2) and are actively synthesized by cells in culture (3). These proteoglycans have been found to be present on the plasma membrane and in the extracellular matrix (4, 5) and exhibit a peculiar structural variability according to the tissue and species of origin (2, 6). Despite their wide occurrence, little is known of their biological function. They have been implicated in several biological processes such as cell-cell recognition (7), tissue differentiation (8), organization of extracellular matrices (9), and cell-matrix and cell-substrate adhesion (10). The availability of two heparitinases (11, 12) and a heparinase (EC ) from Flavobacterium heparinum (12, 13), which can be used in conjunction to elucidate the distribution and grouping in the polymeric chain of disaccharides with various degrees of sulfation and with different hexuronic acid moieties, has enabled us to undertake the structural study of a proteoglycan isolated from the conditioned medium of endothelial cell cultures that appears to be highly characteristic of this cell type. Using these enzymes, we have determined that the glycosaminoglycan chain of this proteoglycan contains heparin segments and have developed a strategy for the elucidation of the sequence of the disaccharide repeating units that may be applicable to the study of other structurally related compounds. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C solely to indicate this fact. MTERILS ND METHODS Substrates, Enzymes, and Materials. Heparin from bovine intestinal mucosa and heparan sulfate from bovine pancreas were gifts from P. Bianchini (Opocrin Research Laboratories, Modena, Italy). Chondroitin 4- and 6-sulfates were purchased from Miles. Heparinase, heparitinases, disaccharide sulfoesterase, and glycuronidase were prepared from induced F. heparinum cells, and mono-, di-, and tetrasaccharides were prepared from heparin and heparan sulfates as described (11-13). Ethylenediamine (1,2-diaminoethane) was purchased from ldrich. L-[ring-2,3,4,5,6-3H]phenylalanine (106.3 Ci/mmol; 1 Ci = 37 GBq), D-[1,6-3H(N)]glucosamine hydrochloride (42.5 Ci/mmol), and carrier-free [35S]sulfuric acid were purchased from New England Nuclear. Preparation of the Heparan Sulfate Proteoglycan (HSPG) Synthesized by Endothelial Cell Cultures. n established endothelial cell line derived from rabbit aorta (14) was used for these studies. To obtain proteoglycans labeled in their carbohydrate moieties, postconfluent cell cultures were incubated for hr in F-12 tissue culture medium supplemented with 5% fetal bovine serum and either 150 uci of carrier free [35S]sulfuric acid or 10,uCi of [35S]sulfuric acid and 10,Ci of [3H]glucosamine per ml. Proteoglycans labeled in their protein core were obtained by supplementing the culture medium with 10,Ci of [3H]phenylalanine per ml. The HSPG was isolated from the conditioned medium by Sepharose CL-6B gel filtration followed by ion-exchange chromatography on DEE-cellulose as described (15). When indicated, protein-free heparan sulfate glycosaminoglycan chains were prepared from the proteoglycan by incubation with 0.1 mg of Superase (protease from Pfizer) per ml for 4 hr at 60 C. fter incubation the mixture was heated for 7 min at 100 C, and the radiolabeled glycosaminoglycan was precipitated with 2 volumes of methanol at -20 C in the presence of carrier heparan sulfate. Enzymatic Degradation of the Glycosaminoglycan Chains of the HSPG. typical incubation mixture contained 0.1 unit of enzymes, x 103 cpm of HSPG with 50,ug each of heparan sulfate and heparin, and other additions as indicated in 0.05 M ethylenediamine acetate buffer (ph 7.0) in a final volume of 30 ul. The incubation mixtures were spotted in Whatman no. 1 paper and subjected to chromatography in isobutyric acid/1 M NH3, 5:3 (vol/vol), or isobutyric acid/ 1.25 M NH3, 5:3.6, for 48 hr. Electrophoresis of the degradation products was performed in Whatman 3MM paper in 0.25 M (NH4)HCO3 buffer (ph 8.5). The unsaturated pro- bbreviations: Ido, iduronic acid; Ido, 0-(4-deoxy-hex-4-enopyranosyliduronic acid; Ido-2S, Ido 2-sulfate; Glc, glucuronic acid; Glc, 0-(4-deoxy-hex-4-enopyranosylglycuronic acid; GlcNS, 2-sulfamino-D-glucose; GlcNS-6S, GlnNS 6-sulfate; Gln- Nc, 2-acetamido-D-glucose; GlcNc-6S, GlcNc 6-sulfate; (1-4), glycosidic linkage (1--4); HSPG, endothelial cell heparan sulfate proteoglycan. *On leave from Departamento Bioquimica, Escola Paulista de Medicina, C.P Sao Paulo, S.P. Brazil.

2 3566 Biochemistry: Nader et Proc. Natl. cad. Sci. US 84 (1987) * _ HEPRIN _ CHONDROrTIN SULFTE.* HEPRN SULFTE - ig~c(1-4)glcnc-6s K GIc(1-4)GIcNS GIcNS-6S from e Ido01-4)GlcNS-6S ORIGIN _SUPERSE HTSE I HEPSE NONE ENYME FIG. 1. Electrophoretic behavior of HSPG and its heparinase and heparitinase I degradation products. bout 20,000 cpm of [31S]HSPG was incubated with Superase (lanes +), a proteolytic enzyme, or with buffered solution containing protease inhibitors (lanes -) in the presence of 50,ug of carrier heparan sulfate for 2 hr at 60 C in a final volume of 20.l. The incubation mixtures were then heated at 100 C for 7 min. To the mixtures, 0.1 unit ofheparinase (HEPSE), 0.1 unit of heparitinase I (HTSE I), or buffer (NONE) were added, and the mixtures were incubated further for 3 hr in 0.05 M ethylenediamine acetate buffer (ph 7.0) at 30 C in a final volume of 30,ul. liquots (5,ul) were applied to the agarose gel and subjected to electrophoresis in 0.05 M sodium phosphate buffer (ph 8.5) for 30 min at 120 V. fter fixing and staining, a radioautogram was prepared by exposing the dried gel to x-ray film. Lane St shows a standard mixture of heparan sulfate, chondroitin sulfate, and heparin. ducts formed were detected by short-wave UV lamp. The radioactive 35S-labeled products were located by exposure of the chromatograms to Kodak x-ray film (SB-5) for 3-15 days. They were quantitated by assaying the paper containing the radioactive compounds in 0.5% 2,5-diphenyloxazole in toluene in a liquid scintillation spectrometer. One of the products, 0-(4-deoxy-hex-4-enopyranosylglycuronic acid)-(1-. 4)-2-acetamido-D-glucose [Glc(1-4)GlcNc] contains only [3H]glucosamine and was located with the help of the same disaccharide formed from the carrier heparan sulfate by action of heparitinase I (see below). Fractionation of HSPG Degradation Products Prepared by the ction of the Enzymes. bout 50,000 cpm of [3H]glucosamine and [35S]HSPG with carriers heparin and heparan sulfate (100,g) were incubated with 0.1 unit of heparinase in the presence of 0.02 M MnCl2 or heparitinase I in a final volume of 50 l as described above. fter incubation 500 jig of heparan sulfate was added to the mixture and applied to a Sephadex G-50 superfine column (1 x 120 cm) previously equilibrated with 1 M acetic acid. The products were eluted from the column in 1-ml fractions with 1 M acetic acid. liquots of the different fractions (see below) were used to determine the amount of radioactivity present, and the different peaks obtained were combined, lyophilized, and subjected to enzymatic analyses. Other Methods. N-desulfation of [35S]HSPG and [3H]glucosamine-labeled HSPG was performed in 0.04 M HCl at 100 C for 2 hr in the presence of carrier heparan sulfate. garose gel electrophoresis in phosphate buffer was performed as described (16). RESULTS Most of the structural studies reported in this paper are based on the specificities of the enzymes prepared from Flavobacterium heparinum. Their action has been studied in detail by different laboratories (for a review, see ref. 17). Briefly, the heparinase acts upon glucosaminido-iduronic acid link- Ido-2S(1-4)GlcNS + * a.gic(1-4)glcns-6s * V -.1Ido-2S(1-4)GlcNS-6S 9 - Unknown _ K_ Ido-2S(1-4)GlcNS-6Sj *g L Glc(1-4)GlcNS-6S Origin FIG. 2. Degradation products formed from [35S]HSPG by action of heparinase, heparitinase II, and heparitinase I. bout 20,000 cpm of [35S]HSPG in the presence of 100,ug of carrier heparan sulfate were incubated with 0.1 unit of heparitinase I (lane 1) or heparinase/glycuronidase (lanes 2 and 3) or in the absence of enzymes (lane 4) in 0.05 M ethylenediamine acetate buffer (ph 7.0) in a final volume of 30 1.l for 4 hr at 300C. fter incubation, the mixtures were heated at 100'C for 1 min, and 0.1 unit of heparitinase II was added to lanes 1 and 3. The mixtures were incubated an additional 4 hr at 30 C. The incubation mixtures were applied to Whatman no. 1 filter paper and chromatographed for 48 hr with isobutyric acid/1.25 M NH3, 5:3.6 (vol/vol), as the descending solvent. radioautogram was then prepared from the chromatogram with x-ray film. ages where the glucosamine is sulfated at the 2 position. The heparitinase I is specific for N-acetyl or N-sulfate glucosaminido-glucuronic acid linkages. This enzyme only acts on heparan sulfate regions where the N-acetyl or N-sulfate glucosamine is not sulfated at the 6 position. The heparitinase II is a relatively nonspecific enzyme acting preferentially upon glucosaminido-glucuronic acid linkages where the N- acetyl or N-sulfate glucosamine is sulfated at the 6 position. None of the enzymes act on N-desulfated glucosaminidouronic acid linkages. lso, the disaccharide sulfoesterase and glycuronidase were used to distinguish two types of disulfated disaccharides formed by action of heparinase upon HSPG-O-(4-deoxy-hex-4-enopyranosyliduronic acid 2-sulfate)-(1--4)-2-sulfamino-D-glucose [Ido-2S(1-4)GlcNS] and 0-(4-deoxy-hex-4-enopyranosyliduronic acid)-(1-4)- GlcNS 6-sulfate [Ido(1-4)GlcNS-6S]. Only Ido-2S(1-4) GlcNS is a substrate for the sulfatase producing Ido(1-4) GlcNS. The Ido(1-4)GlcNS-6S is a substrate for the glycuronidase producing GlcNS-6S. For further details see refs and 17. Fragmentation of HSPG by Heparinase, Heparitinase I, and Heparitinase II. The electrophoretic migration of the purified HSPG (before and after proteolysis) as well as the oligosaccharide products formed from this compound by heparinase and heparitinase I are shown in Fig. 1. The heparitinase I oligosaccharides have the same electrophoretic migration as

3 Biochemistry: Nader et al. Proc. Natl. cad. Sci. US 84 (1987) 3567 Table 1. Disaccharides formed by action of heparitinases upon heparinase degradation products of HSPG Mole ratio of disaccharide (disacch.)/fragmentt Ido-2S- Ido-2S- Ido- Glc- Glc- Glc- Glc- Mol of fragment/ (1-4)- (1-4)- (1-4)- (1-4)- (1-4)- (1-4)- (1-4)- Fragment mol of heparan sulfate* GlcNS-6S GlcNS GlcNS-6S GlcNS-6S GlcNc-6S GlcNS GlcNc Oligo Oligo Tetra Tetra Disacch Disacch Disacch *Moles of fragment per mole of heparan sulfate. tno value indicates <0.3 mol/mol of fragment. heparin in this system, whereas the oligosaccharides produced by heparinase have about the same migration of the 31 K.3 intact HSPG. No significant changes in migration were 2' 2 observed by proteolytic treatment of the compounds. These initial experiments suggested that HSPG is a copolymer containing a heparin-like oligosaccharide in a 1 heparan sulfate ' -1 chain. Further analysis of the heparin portion of the glycosaminoglycan chain was performed by using the combined action of,ft n E. I WI -- _ Ln heparinase and glycuronidase. The small molecular weight products formed by action of the enzymes upon [35S]HSPG are shown in Fig. 2. Tetrasaccharides, tri-, and disulfated B OLK;O TETR disaccharides and GlcNS-6S [resulting from Ido(1-4) GlcNS-6S by action of the glycuronidase] are formed from ; ;; HSPG by action of a mixture of these two enzymes. These c4 *0.8 results imply that the heparan sulfate chain of the proteoglycan contains iduronic acid in different regions of its structure 1-80 cv, VĒa *o as in heparin. The trisulfated disaccharide [Ido-2S(1-4) 0..4 x GlcNS-6S], characteristic of heparin, accounts for >10o of U the disaccharides that compose this proteoglycan (Table 1) E. U By combining these enzymes with heparitinases I and II, a decrease of the tetrasaccharides and an increase of tri- and disulfated disaccharides are observed besides the formation of other products (Fig. 2). To gather information on the length and possible distribution of these disaccharide units in HSPG, this material was labeled with [3H]glucosamine and [35S]sulfuric acid, subjected to the action of heparinase, and fractionated by molecularsieving chromatography. Several peaks were obtained after fractionation on Sephadex G-50 (Fig. 3B): two peaks with elution volumes corresponding to two oligosaccharides of Mr =6500 and Mr =3000 and five major peaks with the same elution profiles of tetra- and disaccharides. The fractions containing these different compounds were pooled and subjected to degradation with heparitinases I and II. The types and molar ratios of the disaccharides obtained from each one of the peaks are shown in Table 1. Sequence of the Oligo- and Tetrasaccharides Obtained from HSPG by Heparinase Degradation. Table 1 shows that oligosaccharide 1 contains -1 mol of Ido-2S(1-4)GlcNS-6S, 1 mol of Glc(1-4)GlcNS-6S, and 6 mol each of Glc(1-4) GlcNc and Glc(1-4)GlcNS. The sum of these disaccharides would give a Mr of 6000, which is close to the molecular weight value obtained for this oligosaccharide by gel filtration chromatography with Sephadex G-50. Likewise, the oligosaccharide 2 contains approximately 1 mol each of Ido- 2S(1-4)GlcNS and Glc(1-4)GlcNS-6S, 2 mol of Glc(1-+4)- GlcNc 6-sulfate [Glc(1-4)GlcNc-6S], and 3 mol of Glc(1-4)GlcNS. The sum of these disaccharides gives a Mr of This again is in close agreement with the elution profile obtained for this oligosaccharide by molecular-sieving chromatography. w z n 4(0 0 cn &-l _R~~~V I -..., 4 - C ~~~HEX 00L - 3- D DISCCH ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ FRCTION NUMBER FIG. 3. Fractionation by Sephadex G-50 chromatography of [3H]glucosamine/[35S]-labeled HSPG degradation products formed by the action of the different enzymes. The experiments were performed as described. () Control, HSPG. (B) HSPG with heparinase. (C) Oligosaccharide 1 (fractions from B) with heparitinase I. (D) HSPG with heparitinase I. U, uncharacterized peak; disacch., disaccharide w U., - cv, CD

4 3568 Biochemistry: Nader et al. o-cj Ido-2S-GlcNS-6S OLIGO 1 Ido-2S-GlcNS 5 6 OLIGO 2 ^ Ido-GlcNS-6S * GIc-GlcNS-6S TETR 1 - GIc-GlcNc-6S TETR Y GIc-GIcNS DISCCH 1 X *-0 Glc-GlcNc DISCH?;G DISCCH 3 FIG. 4. Structure of HSPG degradation products formed by action of heparinase. Designations of the glycosidic linkage have been omitted. The uronic acid of the disaccharide located at the nonreducing end is unsaturated. The results shown in Table 1 and Fig. 3 together with the knowledge of the specificity of the heparinase and heparitinases enable one to order the different disaccharides in a specific sequence as shown in Fig. 4. Since the heparinase acts upon glucosaminido-iduronic acid linkages, the unsaturated iduronic acid-containing disaccharides will be located at the nonreducing end of all the fragments. In the case of the tetrasaccharides, the subsequent disaccharide units are at the reducing end as shown in Fig. 4. To assign the next disaccharide unit from the nonreducing end of oligosaccharide 1, the compound was degraded with heparitinase I [which degrades the regions containing Glc(1-4)GlcNS and Glc(1-4)GlcNc] and subjected to molecularsieving chromatography (Fig. 3C). This oligosaccharide was completely degraded to small fragments and disaccharides. The fractions containing the hexasaccharide were combined, further degraded by heparitinase II, and subjected to chromatography on paper. Three disaccharides were identified-namely, Ido-2S(1-4)GlcNS-6S, Glc(1-4)GlcNS-6S, and Glc(1-4)GlcNS in about the same molar ratios. This indicates that Glc(1-4)GlcNS-6S is the vicinal disaccharide of Ido-2S(1-4)GlcNS-6S and is followed by Glc(1-4)GlcNS, which contains the linkage susceptible to heparitinase I (Fig. 4). The disaccharide peak proved to be, by paper chromatography, a mixture of Glc(1-4)GlcNc and Glc(1-4)GlcNS. third smaller peak was eluted between the hexa- and disaccharides (Fig. 3C), and it was not degraded by any of the enzymes, remaining unidentified. To establish the order of the two remaining disaccharide groups, Glc(1-4)GlcNc and Glc(1-4)GlcNS of oligosaccharide 1, the HSPG was N-desulfated by mild acid hydrolysis and subjected to degradation with heparitinase I. The amounts of Glc(1-4)GlcNc formed from this HSPG were comparable to the amounts of this disaccharide formed from a nonhydrolyzed HSPG. This indicates that these disaccharides are clustered in the molecule as shown in Fig. 4. If this were not the case, either no degradation should occur, or N-desulfated tetra- and oligosaccharides should be produced. These results also lead to the conclusion that the remaining disaccharides [Glc(1-4)GlcNS] also have to be vicinal to each other as shown in Fig. 4. O-f0 Proc. Natl. cad. Sci. US 84 (1987) Regarding oligosaccharide 2, the order of Glc(1-4)GlcNc- 6S and Glc(1-4)GlcNS-6S could not be established. Oligosaccharides Obtained from HSPG by Heparitinase I Degradation. The results of the chromatographic analysis of the products formed from HSPG by heparitinase I are shown in Fig. 3D. Two main peaks were eluted at the volumes corresponding to Mr 3500 and 3000 plus another main peak in the disaccharide region. s expected, analyses of the disaccharide peak by paper chromatography revealed a mixture of Glc(1-4)GlcNS and Glc(1-4)GlcNc. The fractions containing the two main oligosaccharides were combined and degraded by heparinase followed by heparitinase II. The type and amount of products formed from these compounds by the combined action of the enzymes is shown in Table 2. Heparin-Like Regions of HSPG. The results shown in Fig. 3D suggests that the oligosaccharides with Mr 3500 and 3000 contain the heparin-like regions of HSPG. In an attempt to obtain information on the possible sequence of these two segments, the oligo-, tetra-, and disaccharides obtained by heparinase degradation of HSPG (Fig. 4) were assembled in such a way as to include the two main oligosaccharide products formed by the action of heparitinase I from HSPG (Fig. 3D). The combination that best approaches the disaccharide composition of the oligosaccharides (Table 2) together with the sites of action of heparinase and heparitinase I is shown in Fig. 5. In this model two oligosaccharides with Mr 4900 and 4500 could be produced by the action of the heparitinase I. The arrangement of the different tetra- and disaccharides used in the assembly of Fig. 5 is aleatoty, and their proper order could not be established by the present methodology. Distance of Heparin Sequence from the Protein Core of HSPG. To answer this question, HSPG labeled in the protein core with [3H]phenylalanine was degraded with heparitinase I or heparinase and subjected to analysis by agarose gel electrophoresis. s shown earlier (Fig. 1) in this system, the intact proteoglycan migrates with an electrophoretic mobility similar to that of the heparan sulfate chains. If the heparin segment is separated from the protein core by a heparan sulfate type of structure of a sizable length, treatment with heparinase should affect the mobility of the protein core only to a limited extent. Conversely, treatment with heparitinase I should effectively decrease the amount of tritium label in the heparan sulfate area of the agarose gel if the segment of glycosaminoglycan close to the glycopeptide linkage is represented by an N-acetylated region typical of heparan sulfate. The results of these experiments have shown that, only after heparitinase I degradation, there is a marked reduction of the amount of label present in the heparan sulfate region, suggesting that the heparin oligosaccharides are separated from the core protein by a heparan sulfate region. DISCUSSION Iduronic acid-containing tri- and disulfated disaccharides and tetra- and pentasulfated tetrasaccharides typical of heparin are also conspicuously present in the HSPG of rabbit endothelial cells in culture. s judged by the amounts of unsaturated products formed by the action of heparinase Table 2. Disaccharide products formed from heparitinase I-digested oligosaccharides (oligo.) by action of heparinase and heparitinase II Mole ratio of disaccharide/fragment Ido-2S- Ido-2S- Ido- Glc- Glc- Glc- (1-4)- (1-4)- (1-4)- (1-4)- (1-4)- (1-4)- Fragment GlcNS-6S GlcNS GlcNS-6S GlcNS-6S GlcNc-6S GlcNS Oligo Oligo

5 Biochemistry: Nader et HEPRMNSE I HEPRITINSE I Proc. Natl. cad. Sci. US 84 (1987) 3569 HEPRITINSE I T I T HEPRINSE 4,870 r t t HEPRINSE FIG. 5. Proposed structure of HSPG and sites of action of heparinase and heparitinase I. R, protein core. Symbols are the same as in Fig. 4, and the molecular weights are indicated. upon HSPG, -20% of the molecule contains iduronic acid residues. mong >20 heparan sulfates from different mammalian and invertebrate tissues and species analyzed by the same methodology (2, 6), this is the only heparan sulfate extensively susceptible to heparinase. The iduronic acidcontaining disaccharides are clustered in two sulfate-rich oligosaccharide areas separated from the protein core by a N-sulfated and N-acetylated region. The specificity of action of heparinase and heparitinase I has made it possible to order most of the disaccharides that compose the HSPG in a specific sequence as shown in Fig. 5. The total number of disaccharides found in these analyses suggests that the heparan sulfate has a Mr of -15,000. Nevertheless, the average molecular weight of the intact heparan sulfate chain (after proteolysis or P-elimination) is in the order of 55,000 (unpublished results). This implies that four of the units shown in Fig. 5 should constitute the heparan sulfate chain. t present no information is available about how these four units are assembled. Perhaps some clues could be obtained when the structure of the sulfated unknown product formed by the joint action of the enzymes upon HSPG (Figs. 2 and 3C) is obtained. This compound accounts for 3% of the total sulfated products formed by the action of the enzymes (about 1 mol of compound per mol of the Mr 15,000 unit), has an elution position in Sephadex of a disaccharide, and is not degraded by the glycuronidase or the disaccharide sulfoesterase. This could be an indication that this "disaccharide" is situated at the nonreducing end of the chains, since these enzymes do not act upon saturated disaccharides. If this alternative proves to be correct, we have to consider the possibility that each of the four units is linked directly to a peptide core resistant to proteolysis and a-elimination. lternatively, our data do not rule out the possibility that the carbohydrate chains are branched. Iduronic acid-containing disaccharides have been reported to be present in heparan sulfate species obtained from different tissues (18, 19) and from cultured microvascular endothelial cells (20). In these microvessel-derived cultures, as it had been reported for the established endothelial cell line (15, 21) used in the present studies, heparan sulfate proteoglycans exhibited anticoagulant activity. The methodology outlined in this report may prove useful for the characterization of the structural features of the glycosaminoglycan chain responsible for biological activity. 4,460 t This work was aided by grants from Fundacao de mparo a Pesquisa do Estado de Sao Paulo, Conselho Nacional de Desenvolvimento Cientifico e Tecnol6gico, Brazil, and by grants from the Council for Tobacco Research (no. 1414) and R. J. Reynolds, Inc. 1. Roden, L. (1980) in The Biochemistry of Glycoproteins and Proteoglycans, ed. Lennarz, W. J. (Plenum, New York), pp Nader, H. B., Ferreira, T. M. P. C., Paiva, J. F., Medeiros, M. G. L., Jer6nimo, S. M. B., Paiva, V. M. P. & Dietrich, C. P. (1984) J. Biol. Chem. 259, Dietrich, C. P. & Montes de Oca, M. (1970) Proc. Soc. Exp. Biol. Med.. 134, Kraemer, P. M. (1971) Biochemistry 10, Gowda, D. C., Bhavanandan, V. P. & Davidson, E.. (1986) J. Biol. Chem. 261, Dietrich, C. P., Nader, H. B. & Straus,. H. (1983) Biochem. Biophys. Res. Commun. 111, Dietrich, C. P., Sampaio, L. O., Toledo, 0. M. S. & Cassaro, C. M. F. (1977) Biochem. Biophys. Res. Commun. 75, Kinoshita, S. & Saiga, H. (1979) Exp. Cell Res. 123, Ogston,. G. (1970) in Chemistry and Molecular Biology of the Intracellular Matrix, ed. Balazs, E.. (cademic, New York), Vol. 3, pp Laterra, J., nsbacher, R. & Culp, L.. (1980) Proc. Natl. cad. Sci. US 77, Silva, M. E., Dietrich, C. P. & Nader, H. B. (1976) Biochim. Biophys. cta 437, Silva, M. E. & Dietrich, C. P. (1975) J. Biol. Chem. 250, Dietrich, C. P., Silva, M. E. & Michelacci, Y. M. (1973) J. Biol. Chem. 248, Buonassisi, V. & Venter, J. C. (1976) Proc. Natl. cad. Sci. US 73, Buonassisi, V. & Colburn, P. (1982) nn. N. Y. cad. Sci. 401, Jaques, L. B., Ballieux, R. E., Dietrich, C. P. & kavanagh, L. W. (1968) Can. J. Physiol. Pharmacol. 46, Dietrich, C. P., Michelacci, Y. M. & Nader, H. B. (1980) in Mechanism of Saccharide Polymerization and Depolymerization, ed. Marshall, J. J. (cademic, New York), pp Cifonelli, J.. & Dorfman,. (1960) J. Biol. Chem. 235, Linker,. & Hovingh, P. (1974) Carbohydr. Res. 37, Marcum, J.. & Rosenberg, R. D. (1985) Biochem. Biophys. Res. Commun. 126, Colburn, P. & Buonassisi, V. (1982) Biochem. Biophys. Res. Commun. 104, , and erratum (1982) 105, 791.